The present invention relates to a nuclear magnetic resonance (NMR) system that enables multiplex resonance measurement which generates a plurality of frequencies at the same time and measures the resonance of a plurality of nuclears.
For the purpose of enhancing the resolution of a nuclear magnetic resonance (NMR) spectroscopy, there has been developed the NMR system that is capable of supplying a high frequency signal with a high resonance frequency under a uniform high magnetic field (B0). In order to generate a high magnetic field of 10 or higher tesla (T), a superconductivity magnet is generally employed. Currently, there has been developed a high magnetic field NMR system mainly intended for structural analysis of protein material, and an NMR system of 21.6 T (920 MHz) is produced. In order to achieve analysis with high precision, it is necessary to enhance the uniformity of a magnetic field intensity, and it is desirable that a variation of the magnetic field intensity in a region where a sample to be measured exists is 10−9 or less.
On the other hand, a high sensitivity is demanded for a probe that receives a free induction decay (FID) signal generated according to a supplied high frequency pulse. This is because in the case where the amount of sample is small as with protein material, the FID signal intensity is particularly low, and a long period of time is required for measurement. The main noise in the probe is derived from an electric resistance of the probe that constitutes a resonator, and depends on the temperature and the high frequency loss resistance of the material. In order to reduce the noise, a probe coil and a preamplifier are located at a low temperature, and there is used a high temperature superconductivity material that is lower in the high frequency loss resistance than normal metal such as copper by two figures or more, as disclosed in U.S. Pat. No. 5,247,256.
An example using the high temperature superconductivity material for the probe coil is disclosed in U.S. Pat. No. 5,585,723. A thin film is used as the superconductivity material, and a film surface is required to be arranged in parallel with a direction of a static magnetic field. This is because when the film surface of the superconductivity material is located in a direction orthogonal to the static magnetic field, the uniformity of the static magnetic field intensity is deteriorated by a full diamagnetic characteristic of the superconductivity material.
Also, it is necessary that the probe coil is arranged in such a manner that the high frequency magnetic field is orthogonal to the static magnetic field when an electricity is fed to the probe coil. Since a sample tube into which a sample to be measured is incorporated is inserted in a vertical direction, the following arrangement is used.
In the following description, an NMR system using the superconductivity magnet that generates a static magnetic field in a horizontal direction is called “horizontal NMR system”, and an NMR system using the superconductivity magnet that generates a static magnetic field in a vertical direction is called “vertical NMR system”.
FIGS. 1A to 1C show a conventional horizontal NMR system, in which FIG. 1A is a perspective view of a superconductivity solenoid coil 11, FIG. 1B is a perspective view of a saddle coil 12, and FIG. 1C is a perspective view showing the arrangement of the superconductivity solenoid coil 11 and the saddle coil 12.
FIGS. 2A to 2C show a conventional vertical NMR system, in which FIG. 2A is a perspective view of a superconductivity solenoid coil 21, FIG. 2B is a perspective view of a saddle coil 22, and FIG. 2C is a perspective view showing the arrangement of the superconductivity solenoid coil 21 and the saddle coil 22.
In the horizontal NMR system whose static magnetic field direction 3 is horizontal, the solenoid coil 11 shown in FIG. 1A is used as a reception probe coil. In the vertical NMR system whose static magnetic field direction 3 is vertical, the saddle coil 21 shown in FIG. 2A is used as the reception probe coil.
In the case where the probe coil is made of normal metal, there are many cases in which the probe coil transmits and receives the high frequency magnetic field.
On the other hand, in the case where the probe coil is formed of a superconductivity thin film, there are many cases in which the probe coil is used for only receiving the high frequency magnetic field since the superconductivity thin film does not withstand a large high-frequency current. In this case, a saddle coil is disposed outside of the probe coil for transmission of the high frequency magnetic field.
From the above-mentioned restrictions, in the horizontal NMR system, the reception probe coil 11 and the transmission probe coil 12 are arranged as shown in FIG. 1C. In the vertical NMR system, the reception probe coil 21 and the transmission probe coil 22 are arranged as shown in FIG. 2C. In order to prevent the reception coil from electromagnetically interfering with the transmission coil, it is necessary to dispose the probe coil so that the high frequency magnetic fields that are developed in the centers of the respective reception coil and transmission coil when electricity is fed to those coils are orthogonal to each other.